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As the latest iPhone went on sale Friday, with T-Mobile USA once again left out of the party, the fourth-place U.S. carrier started turning on a network that is designed to offer high data rates on unlocked iPhones.

On Friday, T-Mobile launched commercial service in Las Vegas on an HSPA+ 3G network that uses frequencies around 1900MHz, a band that's available on unlocked iPhones. T-Mobile CTO Neville Ray announced the launch during an appearance at the GigaOm Mobilize conference in San Francisco. Las Vegas is the first city to get the new network, in a rollout that will reach other markets by 2013, he said.

The launch is part of a larger strategy by T-Mobile to effectively become an iPhone carrier without winning a deal to carry new iPhones in its stores. To that effect, it's also demonstrating iPhones in its stores, even though it doesn't sell them, and developing apps for iOS such as billing and voicemail.

T-Mobile estimates there are more than 1 million unlocked iPhones on its network already. The underdog carrier says it can offer consumers a better deal on service, with unlimited data. "We're going to bring a lot more iPhones to our network with what we're doing," Ray said in an interview following his appearance on stage.

In smartphones with the right radios, such as the iPhone 5, the HSPA+ network can deliver average download speeds of 8Mbps to 10Mbps, which is in the same ballpark as some LTE services, according to Ray. All of the iPhone's official carriers offer 4G LTE service in at least sone cities, addition to 3G service; LTE speeds can be as fast as 30Mbps. T-Mobile is converting the 1900MHz spectrum from an older, slower GSM network to the new system, Neville said.

The company's focus is on the HSPA+ rollout now, but next year it plans to launch commercial LTE service. That new network, which will be built with the so-called LTE Advanced system in version 10 of the standard, will provide faster performance than HSPA+, Ray said, but he declined to predict its speed.